U-tube stabilizer having adjustable crossover duct and end chambers

ABSTRACT

A passive U-tube stabilizing tank adjustable in frequency for matching the natural frequency of the tank to the natural roll frequency of an associated vessel. The stabilizing tank is filled to a predetermined level with stabilizing liquid, above the level of the crossover duct. The effective length of the crossover duct, and the effective length of the respective end chambers are variable by means of horizontally oriented gate valves cooperating with a plurality of vertical plates located in the end chambers. The natural frequency of the tank is varied by moving the gate valves with respect to the vertical plates.

United States Patent 1 Corvino et al.

[ 51 Nov. 27, 1973 [75] Inventors: Ralph A. Corvino, Spring Valley,

N.Y.; John P. Martin, Upper Montclair, NJ.

[73] Assignee: Flume Stabilization Systems, Inc.,

Hoboken, NJ.

[22] Filed: Nov. 26, 1971 [21] Appl. No.: 202,497

37,220 3/1965 East Germany ..l14/125 Primary ExaminerMilton BuchlerAssistant Examiner-Galen L. Barefoot 7 Att0rneyMartin Fleit et al.

[5 7] ABSTRACT A passive U-tube stabilizing tank adjustable in frequencyfor matching the natural frequency of the tank to the natural rollfrequency of an associated vessel. The stabilizing tank is filled to apredetermined level with stabilizing liquid, above the level of thecrossover duct. The effective length of the crossover duct, and theeffective length of the respective end chambers are variable by means ofhorizontally oriented gate valves cooperating with a plurality ofvertical plates located in the end chambers. The natural frequency ofthe tank is varied by moving the gate valves with respect to thevertical plates.

8 Claims, 3 Drawing Figures [52] U.S.Cl. 114/125 [51] Int. Cl B63b 43/06[58] Field of Search 114/121, 122, 125

[56] References Cited UNITED STATES PATENTS 3,487,801 l/l970 Calvi114/125 3,606,851 9/1971 Pangalila et a]. ll4/l25 FOREIGN PATENTS ORAPPLICATIONS 657,233 2/1938 Germany 114/125 INVENTORS Ralph A. Corv/noJohn PMor/m BY ATTORNEYS PATENIED NOV 27 I975 U-TUBE STABILIZER HAVINGADJUSTABLE CROSSOVER DUCT AND END CHAMBERS BACKGROUND OF THE INVENTIONThe U-tube stabilizer had long been known in the prior art as a deviceuseful in counteracting the roll of watergoing vessels. Such aconnected" dynamic system is intended to operate so that the tank liquidoscillates substantially 90 out of phase with the driving force, in thiscase, the roll of the ship. In this manner, the liquid in the endchambers of the U-tube acts to counteract the roll of the ship.

The passive U-tube stabilizer is not, however, without itsdisadvantages. During various sea states, and under varying loading, aships roll often changes in its natural frequency from its calculated orobserved natural frequency at the design condition. In fact, a shipoften rolls at natural frequencies quite far removed from the designnatural frequency. While the damped freesurface tank is able tosuccessfully cope with such changes in roll frequency, the U-tube isordinarily not. With the known U-tube stabilizers oscillated at otherthan the design frequency, the phase lag will be somewhat higher orlower than 90 and hence the stabilizing effect is diminished to someextent. In some extreme cases the oscillation of the liquid may evencause a destabilizing rather than a stabilizing effect on the ship.

There are known passive stabilizers which attempt to vary the frequencyof the U-tube to match the varying roll frequency of the ship. Thestabilizers typically provide a valved air cross-connection between theupper ends of the two chambers, where changes in the valving controlsthe liquid oscillation in the U-tube. While these devices are to someextent capable of changing the U-tube frequency, they are known togreatly restrict the transfer of liquid between the end chambers. Therise and fall of liquid in the end chambers tends to be insufficient toprovide the significant force necessary to counteract the roll of theship.

It is toward the elimination of the above-notedproblems that the presentinvention is directed.

SUMMARY OF THE INVENTION The present invention relates to a U-tubestabilizing tank equipped, for the first time, with means for matchingthe U-tube frequency to the frequency of roll of the ship withoutdegrading the stabilizing effect of the tank.

It has been foundthat the natural frequency of liquid transfer within aU-tube stabilizer is a function of the relative lengths of the crossoverduct and the end chambers. The natural frequency of oscillation ofliquid in a U-tube stabilizing tank increases as the length of thecrossover duct decreases. The tank of the present invention is,basically, a U-tube stabilizer comprising two end chambers connected attheir lower ends by means of a crossover duct. A series of horizontallyspaced vertical plates are secured to the inner walls of the respectiveend chambers and run coextensive thereto, separating each end chamberinto a series of horizontally spaced vertical channels.

In the preferred embodiment of the present invention, a horizontallyoriented gate valve is slidably mounted on the inner walls of thecrossover duct adjacent the upper wall thereof. The respective gatevalves are adapted to travel horizontally and selectively close from thebottom, one or more of the vertical channels of the end chambers. Byclosing selected vertical channels, the effective length of thecrossover duct is thereby increased, while the effective length of eachend chamber is correspondingly decreased. The flow of tank liquid isrestricted to those channels not sealed by the gate valves.

By changing the liquid flow from one end chamber to the other inaccordance with the teachings of the pres ent invention, the frequencyof oscillation of the liquid is altered. Yet there is substantially nochoking effect on the free transfer of stabilizing liquid as there is anunrestricted uniform area crossover duct through which the stabilizingliquid flows and unrestricted uniform area end chambers into which thestabilizing liquid flows. This capability enables the frequency of theU-tube stabilizer to be matched to the frequency of the roll of the shipwithout detracting from the stabilization effects. And the number ofdistinct frequencies of oscillation is a function only of the number ofvertical channels provided. When the roll frequency of the ship changesdue to varying loading conditions or sea states, the gate valves aresimply activated and positioned so as to match the natural frequency ofoscillation of the tank to the roll of the ship, thereby maintaining thedesired phase relationship between the ships roll and the liquidoscillation, without substantially affecting the transfer of tankliquid.

Accordingly, it is the main object of the present invention to provide apassive U-tube stabilizer which may be quickly and efficiently matchedin frequency to the roll frequency of the associated vessel.

It is a further object of the present invention to provide a passiveU-tube stabilizer whose natural frequency may be incrementally variedover a relatively wide range of frequencies.

It is yet a further object of the present invention to provide a passiveU-tube stabilizer whose natural frequency can be varied without changingthe liquid level in the tank.

Still a further object of the present invention is to provide a passiveU-tube stabilizer whose natural frequency may be incrementally varied bychanging the length of the crossover duct and the lengths of the endchambers.

These and other objects of the present invention, as well as many of theattendant advantages thereof, will become more readily apparent whenreference is made to the following description taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an enlarged cross-sectionalview of the inventive variable frequency U-tube stabilizer;

FIG. 2 is a sectional view of the inventive stabilizer taken along line2-2 of FIG. 1; and

FIG. 3 is a sectional view taken along the line 33 of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS With reference to FIGS. 1 through3, the inventive variable frequency U-tube stabilizer tank will bedescribed. The U-tube stabilizer is shown generally at 10 and comprisestwo end chambers 20 and 22 interconnected at their respective lower endsby a horizontal crossover duct 24. As shown in the figures, two verticalplates 26 and 28 are fixedly secured to the top inner walls 33 of therespective end chambers 20 and 22, each plate extending entirely acrossthe width and substantially the entire height of the end chambers. Thevertical plates 26 and 28 are arranged parallel to the longitudinalbulkhead components of the end chambers, and define a series of threevertical chambers 30, 32 and 34 within each end chamber. A liquid 36 ishoused in the stabilizer l and oscillates between end chamber and endchamber 22, being transferred through the crossover duct 24. Thevertical plates 26 and 28 extend to the respective tops of the endchambers and terminate at their lower ends substantially at the level ofthe top of the crossover duct 24. A set of three vents 38 is provided atthe top of each upstanding end chamber, with one vent in each of thethree verti cal channels 30, 32 and 34, to prevent pressure buildup inthe end chambers when the liquid 36 ocillates in the tank 10.

A gate valve arrangement shown generally as 40 in provided at each endof the crossover duct 24 and associates with the respective end chambers20 and 22. The gate valves 40 are capable of restricting the flow ofliquid 36 through one or more of the sets of channels 30, 32 and 34.Each gate valve 40 comprises a door 42 slidably mounted on a set oftracks 44 secured to the inner wall 31 of the crossover duct 24, as mostclearly illustrated in FIG. 3. The doors 42 are horizontally andsimultaneously moved by means of a winch 46 and a pair of cables 48. Asseen in FIGS. 1 and 2, each cable 48 is continuous, is controlled by thewinch 46, and is attached to the associated door 42 at both endsthereof. A pulley arrangement 50 is secured at each end of the tank 10,substantially at the height of the respective gate valves 40, and servesto reverse the direction of the cable 48. Hence, by activating the winch48, the cables 48 act on the respective doors 42 to adjust the positionsof the doors relative to the vertical plates 26 and 28. As can best beseen in FIG. 2, the cables 48 associate with the winch 46 so that therespective doors 42 move simultaneously and in the same sense.

When the doors 42 are in the positions illustrated in FIGS. 1 and 2, thedoors contact only the vertical plates 28, thereby substantially sealingoff only the most inboard channel 30. But it should be appreciated thatthe doors can be moved further outboard to contact both vertical plates26 and 28, thereby sealing off .the two most inboard channels and 32,thereby deactivating the tank entirely. Or the doors could be completelyretracted from the regions of the end chambers to make full use of thelengths of the end chambers. It should be apparent therefore, that theinventive tank is extremely versatile, and that the number and range ofincremental frequencies of oscillation for matching the frequency of thetank to that of the ship may be varied by changing the number andspacing of the vertical plates 26 and 28.

Now, the function of the gate valves and the vertical plates of theinventive U-tube stabilizer tank 10 will be described. With the gatevalves 40 in their fully opened position, liquid oscillates through thecrossover duct and is free to pass into any of the three verticalchannels 30, 32, and-34 of the end chambers. The effective lengths ofthe crossover duct under these conditions is represented by w, in FIG.1; and the corresponding frequency of oscillation is f,. As actuallyshown in FIG. I, the gate valves 40 have been moved outboard so as toabut the first vertical plate 28. Liquid oscillating through thecrossover duct may therefore enter only through the most outboard two ofthe vertical channels 32 and 34, with substantially no liquid enteringthe most inboard channel 30. The effective length of the crossover ductis therefore W2; and the U- tube then has a natural frequency f With thegate valves moved to abut the second vertical plate 26, liquid cantransfer only through the most outboard of the vertical channels 34. Thecrossover duct is therefore increased in length to W3; and the naturalfrequency of the tank becomes f Naturally, with the gate valves in theirmost outboard position, complete deactivation of the U-tube system isaccomplished, such gate valve positioning being useful when the loadingcondition or sea state causes the ship to roll at frequencies so farremoved from the frequency band of the inventive stabilizer thatstabilization cannot be practiced.

The vertical plates 26 and 28 are substantially evenly spaced from theinboard and outboard walls of the end chambers. And the tank is designedso that with the gate valves in one of their intermediate positions, thetank is matched to the average roll frequency of the ship. Then, if theroll frequency of the ship changes due to loading conditions or seastate, the gate valves are adjusted accordingly. As mentionedpreviously, the natural frequency of oscillation of the liquid in a U-tube stabilizing tank increases as the length of the crossover ductdecreases. And since w w w f, f f Therefore, in order to increase thenatural frequency of the inventive stabilizing tank, as may be necessaryafter the ships cargo has been discharged, the valve gates should bemoved inboard.

Above, the preferred embodiment of the present in vention has beendescribed. In such an embodiment, a passive U-tube stabilizer isequipped with means for quickly and simply varying the relative lengthsof the crossover duct and the end chambers, thereby bringing about achange in the natural frequency of the tank and permitting the matchingof the tank to the roll of the ship over a wide band of rollfrequencies. And while the lengths of the crossover duct and the endchambers are varied to effect a change in the frequency of liquidtransfer, the liquid is still allowed to transfer without restrictionfrom one end of the tank to the other. Accordingly, the frequency of theinvention U-shaped stabilizer may be changed without adversely effectingthe moment developed thereby. A specific embodiment of this inventionhas been described, but for purposes of illustration only. It should beunderstood that many alterations and modifications may be practiced bythose skilled in the art without departing from the spirit or scope ofthe invention. Accordingly, it is the intent that the present inventionnot be limited by the above, but be limited only as defined in theappended claims.

What is claimed is:

1. A passive U-tube stabilizing tank containing a predetermined quantityof stabilizing liquid and particularly suited for use across the beam ofships, the tank comprising: a pair of end chambers; a crossover ductinterconnecting said end chambers near the lower portion thereof, fortransferring said stabilizing liquid between said end chambers, andassociating with said end chambers so as to define a substantiallyU-shaped stabilizing tank; a plurality of vertical channels within eachof said end chambers, plates being secured to the top inner walls ofsaid end chambers, being substantially parallel to the inboard andoutboard walls thereof, and extending from the top of said end chambersdoqnwardly to substantially the top of said crossover duct;

and gate means associating with each of said end chambers and saidplates for selectively blocking all transfer of said stabilizing liquidthrough one or more of said channels in each end chamber, or forentirely retracting from the regions of said end chambers.

2. The stabilizing tank as defined in claim 1, and further comprising:vents in the tops of each channel of said end chambers for preventingpressure buildup in the stabilizing liquid.

3. The stabilizing tank as defined in claim 1, wherein said gate meanslie parallel to and adjacent the top of said crossover duct.

4. The stabilizing tank as defined in claim 1, and further comprisingwinch means for simultaneously and correspondingly moving each of saidgate means.

5. The stabilizing tank as defined in claim 4, wherein said winch meansassociates with first and second cables, the ends of which are connectedto the respective inboard and outboard ends of said gate means.

6. The stabilizing tank as defined in claim 5, wherein said winch andsaid cables are wholly enclosed within the confines of said stabilizingtank.

7. The stabilizing tank as defined in claim I, wherein each gate meanscomprises: a track; a door slidably mounted on said track and adapted totravel substantially perpendicular to said plates; and means for movingsaid door.

8. The method of stabilizing a vessel against roll when the frequency ofroll of said vessel changes substantially, and wherein the vessel isequipped with a liquidhousing passive U-tube stabilizing tank having avariable length crossover duct and variable length end chambers, themethod comprising the steps of: determining the instantaneous frequencyof roll of said vessel; and varying the relative lengths of saidcrossover duct and said end chambers, thereby changing the naturalfrequency of oscillation of said liquid, and thereby matching thefrequency of oscillation of said liquid to the frequency of roll of thevessel. l

1. A passive U-tube stabilizing tank containing a predetermined quantityof stabilizing liquid and particularly suited for use across the beam ofships, the tank comprising: a pair of end chambers; a crossover ductinterconnecting said end chambers near the lower portion thereof, fortransferring said stabilizing liquid between said end chambers, andassociating with said end chambers so as to define a substantiallyU-shaped stabilizing tank; a plurality of vertical channels within eachof said end chambers, plates being secured to the top inner walls ofsaid end chambers, being substantially parallel to the inboard andoutboard walls thereof, and extending from the top of said end chambersdoqnwardly to substantially the top of said crossover duct; and gatemeans associating with each of said end chambers and said plates forselectively blocking all transfer of said stabilizing liquid through oneor more of said channels in each end chamber, or for entirely retractingfrom the regions of said end chambers.
 2. The stabilizing tank asdefined in claim 1, and further comprising: vents in the tops of eachchannel of said end chambers for preventing pressure buildup in thestabilizing liquid.
 3. The stabilizing tank as defined in claim 1,wherein said gate means lie parallel to and adjacent the top of saidcrossover duct.
 4. The stabilizing tank as defined in claim 1, andfurther comprising winch means for simultaneously and correspondinglymoving each of said gate means.
 5. The stabilizing tank as defined inclaim 4, wherein said winch meaNs associates with first and secondcables, the ends of which are connected to the respective inboard andoutboard ends of said gate means.
 6. The stabilizing tank as defined inclaim 5, wherein said winch and said cables are wholly enclosed withinthe confines of said stabilizing tank.
 7. The stabilizing tank asdefined in claim 1, wherein each gate means comprises: a track; a doorslidably mounted on said track and adapted to travel substantiallyperpendicular to said plates; and means for moving said door.
 8. Themethod of stabilizing a vessel against roll when the frequency of rollof said vessel changes substantially, and wherein the vessel is equippedwith a liquid-housing passive U-tube stabilizing tank having a variablelength crossover duct and variable length end chambers, the methodcomprising the steps of: determining the instantaneous frequency of rollof said vessel; and varying the relative lengths of said crossover ductand said end chambers, thereby changing the natural frequency ofoscillation of said liquid, and thereby matching the frequency ofoscillation of said liquid to the frequency of roll of the vessel.